Intracellular recordings from neurons in the abdominal ganglial of Aplysia have been performed using two intracellular glass microelectrodes. One electrode is used primarily for recording of intracellular events while the other electrode is used for passing direct currents. Most of the recordings have been performed on the cell R2 which is basically a silent cell but can also respond with an EPSP by stimulation of a major connective. Parameters evaluated include resting membrane potential and conductance, spontaneous spike activity, spike configuration, and EPSP thresholds and configuration. Test solutions have included normal and hypertonic saline, 10% solutions of sodium diatrizoate, meglumine iothalamate, and metrizamide. The results show only a slight depolarization of resting membrane potential by sodium diatrizoate and meglumine iothalamate. There is increase in spontaneous firing produced by all three contrast agents with metrizamide producing the lesser effect. There is no alteration in spike configuration nor in EPSP configurations. Because of this data and previous information suggesting that the primary neurotoxic effect is actually a disinhibition, current experiments are evaluating IPSP's in the cell R15 after stimulation of a major connective. Early experiments indeed show a diminution in IPSP size.